The present invention relates to methods of polishing intraocular lenses. More specifically, the present invention relates to methods of dry polishing intraocular lenses in a bed of particles to remove flash, surface irregularities and/or sharp edges from molded or lathe cut surfaces thereof.
Methods of molding articles from moldable materials have been known for some time. A common problem associated with molding techniques is the formation of excess material or flash on the edges of the molded article. Depending on the type of article formed in the molding process and the manner in which the article is used, the presence of excess material or flash can be undesirable. The same is also true of rough, irregular or sharp edges found on articles produced through a lathing process.
Many medical devices, such as for example intraocular lens implants, require highly polished surfaces free of sharp edges or surface irregularities. In the case of intraocular lenses (IOLs), the lens is in direct contact with delicate eye tissues. Any rough or non-smooth surface on an IOL may cause irritation or abrading of tissue or other similar trauma to the eye. It has been found that even small irregularities can cause irritation to delicate eye tissues.
Various methods of polishing are known in the art. U.S. Pat. Nos. 2,084,427 and 2,387,034 disclose methods of making plastic articles such as buttons that include tumbling the articles to remove projections of excess material or flash.
U.S. Pat. No. 2,380,653 discloses a cold temperature tumbling process to remove flash from a molded article. This method requires the article to be tumbled in a rotatable container of dry ice and small objects such as wooden pegs. The cold temperature resulting from the dry ice renders the flash material relatively brittle, such that the flash is more easily broken from the article during the tumbling process.
U.S. Pat. No. 3,030,746 discloses a grinding and polishing method for optical glass, including glass lenses. The method includes tumbling the glass articles in a composition of liquid, abrasive and small pellets or media. The liquid is disclosed as being water, glycerins, kerosene, light mineral oil and other organic liquids either alone or in combination. The abrasive component is described as being garnet, corundum, boron carbide, quartz, aluminum oxide, emery or silicon carbide. The media is disclosed as being ceramic cones, plastic slugs, plastic molding, powder, limestone, synthetic aluminum oxide chips, maple shoe pegs, soft steel diagonals, felt, leather, corn cobs, cork or waxes.
U.S. Pat. No. 4,485,061 discloses a method of processing plastic filaments which includes abrasive tumbling to remove excess material.
U.S. Pat. Nos. 4,541,206 and 4,580,371 disclose a lens holder or fixture used for holding a lens in a process of rounding the edge thereof. The process includes an abrasive tumbling step.
U.S. Pat. No. 5,133,159 discloses a method of tumble polishing silicone articles in a receptacle charged with a mixture of non-abrasive polishing beads and a solvent which is agitated to remove surface irregularities from the articles.
U.S. Pat. No. 5,571,558 discloses a tumbling process for removing flash from a molded IOL by applying a layer of aluminum oxide on a plurality of beads, placing the coated beads, alcohol, water and silicone IOLs in a container and tumbling the same to remove flash.
U.S. Pat. No. 5,725,811 discloses a process for removing flash from molded IOLs including tumbling the IOLs in a tumbling media of 0.5 mm diameter glass beads and 1.0 mm diameter glass beads, alcohol and water.
Prior methods of removing flash or surface irregularities, such as described above, may be inadequate or impractical in the manufacture of certain types of IOLs. For example, certain IOLs formed from relatively soft, highly flexible material, such as silicone, are susceptible to chemical and/or physical changes when subjected to cold temperatures. For this reason, certain types of cryo-tumbling or cold temperature tumbling may be impractical in the manufacture of IOLs made from such materials. Additionally, certain types of abrasive tumbling processes may be suitable for harder lens material, such as glass or polymethylmethacrylate (PMMA), but may not be suitable for softer lens materials. Also, most tumbling processes known in the art require the lens to be submersed in a liquid that may not be suitable for some lens materials or manufacturing processes. Accordingly, a need exists for a suitable process for removing flash and/or irregularities from molded or lathe cut IOLs made of various materials.
The present invention relates to methods for dry polishing IOLs. IOLs are currently either molded in removable molds or lathe cut. Subsequent to these operations, the IOLs have surface roughness or sharp edges that need to be minimized or eliminated. After polishing methods such as tumbling the IOLs in a container with glass beads and a liquid, the IOLs must be dried or in the case of hydrogels dehydrated, prior to further processing. Drying or dehydrating the IOLs can be both expensive and time consuming. The dry polishing methods of the present invention eliminate the need for drying or dehydrating IOLs. This is particularly important in the case of surface coated IOLs where a coating or surface treatment can not be consistently applied in the presence of moisture.
The method of dry polishing IOLs in accordance with the present invention consists of obtaining a tubular IOL container with two opposed open ends and a number of elongated slots corresponding to the maximum number of haptics on the IOLs to be polished. The tubular IOL container is also equipped with preferably two or more clamps extending from the exterior surface of the IOL container. One or more IOLs are positioned within the IOL container as described in more detail below, so that the IOLs"" haptics extend from the elongated slots formed in the IOL container. The IOL container with IOLs positioned therein is then removably fixed within a polishing chamber. The polishing chamber and the axially concentric IOL tube are preferably maintained in a horizontal position. A volume of dry polishing medium is placed inside the polishing chamber and the one or more open ends thereof removably sealed. The polishing chamber is then axially rotated. As the polishing chamber is rotated, the polishing medium repeatedly contacts the exposed IOL haptic surfaces thus polishing the same. The duration of tumbling and the number of polishing chamber revolutions per minute can be adjusted to achieve the desired degree of polishing. Since the slots of the IOL container protect the IOL optic peripheral edges, the IOL optic peripheral edges remain unpolished and well defined while the remainder is polished. Well-defined peripheral optic edges are desirable to prevent cellular migration and the development of posterior cellular opacification. Following polishing, the IOLs are removed from the polishing chamber and IOL container. The polished IOLs are then easily handled and surface treated without having to dehydrate or dry the same.
Accordingly, it is an object of the present invention to provide a method for dry polishing lathe cut IOLs.
Another object of the present invention is to provide a method for dry polishing molded IOLs.
Another object of the present invention is to provide a method for polishing IOLs without the use of liquids.
Another object of the present invention is to provide a method for polishing IOLs that eliminates the need to dry or dehydrate the same prior to further processing.
Another object of the present invention is to provide a method for dry polishing IOLs that is suitable for a variety of IOL materials.
Still another object of the present invention is to provide a method for polishing IOLs that allows for consistent surface coating without additional process steps.
These and other objectives and advantages of the present invention, some of which are specifically described and others that are not, will become apparent from the detailed description, drawings and claims that follow, wherein like features are designated by like numerals.